NEW YORK (BBC): History will be made on Tuesday when Nasa’s New Horizons probe sweeps past the icy world known as Ultima Thule.
Occurring some 6.5 billion km (4 billion miles) from Earth, the flyby will set a new record for the most distant ever exploration of a Solar System object by a spacecraft.
New Horizons will gather a swathe of images and other data over the course of just a few hours leading up to and beyond the closest approach.
This is timed for 05:33 GMT.
At that moment, the probe will be about 3,500km from Ultima’s surface and moving at 14km/s.
When its observations are complete, the robotic craft will then turn to Earth to report in and begin downlinking the gigabytes of information stored in its memory.
Mission scientists, gathered in a control centre at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, are excited at what lies in prospect.
“It’s electric. People across the whole team are ready. They’re in the game and we can’t wait to go exploring,” says New Horizons’ principal investigator Prof Alan Stern.
The probe is famous for making the first ever visit to the dwarf planet Pluto in 2015. To reach Ultima, it has had to push 1.5 billion km deeper into space.
Virtually nothing is known about this next target for New Horizons, however.
Telescopic measurements indicate it is about 20-30km across, although scientists concede it could actually be two separate entities moving very close to each other, perhaps even touching. The next couple of days will tell.
Ultima is in what’s termed the Kuiper belt – the band of distant, frozen material that orbits far from the Sun and the eight major planets. There are probably hundreds of thousands of Kuiper members like Ultima, and their frigid state almost certainly holds clues to the formation conditions of the Solar System 4.6 billion years ago.
“About one day out we’ll turn on all our instruments,” explains mission scientist Dr Kelsi Singer.